Switching valve

ABSTRACT

The object of the present invention is to provide a switching valve capable of increasing the opening stroke of a valve operated by a differential pressure while saving space, thereby reducing pressure loss. A first valve is disposed between an inlet port and a first outlet port. A pilot valve is provided between a back pressure chamber for a movable plug that holds a valve sheet disposed in a manner opposed to a valve seat, and the first outlet port, such that the first valve is operated by a solenoid. A second valve is arranged between the inlet port and a second outlet port. A back pressure chamber for a movable plug that holds a valve sheet disposed in a manner opposed to a valve seat and the first outlet port are communicated with each other. The second valve is opened by the differential pressure generated by closing of the first valve, and when the first valve is opened, the second valve is closed by the spring since the differential pressure is reduced to zero. After the second valve is closed, the valve-closed state thereof is maintained by the difference between pressure-receiving areas. The second valve is formed to have a sealing structure using a slidable X packing, whereby the valve-opening stroke can be increased.

CROSS-REFERENCE TO RELATED APPLICATIONS, IF ANY

This application is a division of Ser. No. 10/743,439, filed Dec. 23,2003 now U.S. Pat. No. 7,028,713, which application claims priority ofJapanese Application No.2003-000239 filed on Jan. 6, 2003, entitled“Switching Valve” and No. 2003-161572 filed on Jun. 6, 2003, entitled“Switching Valve”.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to a switching valve, and more particularly to aswitching valve for switching a refrigerant passage in a refrigerationcycle of an automotive air conditioner.

(2) Description of the Related Art

In general, in an automotive air conditioner, cooling is carried outusing a refrigeration cycle that circulates refrigerant, and heating iscarried out using engine coolant. Recently, however, due to theimprovement in combustion efficiency of the engine, the temperature ofthe coolant does not rise high enough to a temperature required forheating. As a result, especially when the engine is started in winter,it takes a long time before the temperature in the compartment rises,and there can be cases in which even if the temperature rises, thetemperature does not reach the set-point.

To cope with the above inconvenience, it has been proposed to usehigh-temperature and high-pressure refrigerant discharged from thecompressor in the refrigeration cycle for auxiliary heating (see e.g.Japanese Unexamined Patent Publication No. 2000-318436 (Paragraph No.[0016], FIG. 1)). More specifically, in the refrigeration cycle,high-temperature and high-pressure refrigerant adiabatically compressedby the compressor is first condensed by a condenser, and the condensedrefrigerant is adiabatically expanded by an expansion valve intorefrigerant at low temperature and low pressure. The expandedrefrigerant is evaporated by an evaporator, and then separated into gasand liquid by an accumulator. Gaseous refrigerant obtained by theseparation returns to the compressor. Although the evaporator carriesout heat exchange between the low-temperature refrigerant and the air inthe compartment, to thereby cool the air in the compartment, an attemptis being made to cause the high-temperature refrigerant discharged fromthe compressor to be introduced into the evaporator, to thereby utilizethe evaporator as an air heater for auxiliary heating.

To this end, it is necessary to provide a switching valve on thedischarge side of the compressor, for causing the compressed refrigerantto flow selectively toward the condenser or the evaporator. In aswitching valve of this kind, a first solenoid valve is disposed betweena compressor and a condenser, and a second solenoid valve is disposedbetween the compressor and an evaporator to thereby control the firstand second solenoid valves such that the first solenoid valve is openedand the second solenoid valve is closed during cooling operation, andthe first solenoid valve is closed and the second solenoid valve isopened during heating operation, whereby switching between therefrigerant passages is carried out.

As described above, two solenoid valves are required to switch betweenthe refrigerant passages. However, a switching valve is also known whichperforms the switching operation with one solenoid valve (see e.g.Japanese Unexamined Patent Publication No. 2001-124440 (Paragraph Nos.[0018] to [0023], FIGS. 1 to 3)). According to this switching valve, asolenoid valve for performing opening/closing control of a refrigerantpassage between a compressor and a condenser is integrally formed with adifferential pressure valve that opens a refrigerant passage between thecompressor and an evaporator when the differential pressure between thecompressor and the condenser becomes equal to or larger than apredetermined value, with the above solenoid valve being in a closedstate. The differential pressure valve comprises a valve element forsensing the differential pressure between the compressor and thecondenser, a spring for urging the valve element toward a valve seat,and a diaphragm for sealing between the compressor and the condenser.

In the conventional switching valve of integral construction, however,the sealing mechanism of the differential pressure valve for opening andclosing the refrigerant passage between the compressor and theevaporator is formed by the diaphragm which has small displacementstroke, and hence when an attempt is made to increase the opening strokeof the switching valve so as to reduce pressure loss in the differentialpressure valve, the size of a valve construction is increased.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above points, and anobject thereof is to provide a switching valve in which the openingstroke of a valve operated by a differential pressure is increased whilesaving space, thereby reducing pressure loss.

To solve the above problem, the present invention provides a switchingvalve for causing refrigerant introduced into an inlet port to flowselectively to a first outlet port or a second outlet port,characterized by comprising a first valve that is disposed in a flowpassage between the inlet port and the first outlet port, and controlledby a solenoid, for opening and closing the flow passage, and a secondvalve that includes a valve seat disposed between the inlet port and thesecond outlet port, a valve element capable of moving to and away fromthe valve seat, a passage for introducing pressure from the first outletport to a surface of the valve element opposite to a surface of thevalve element opposed to the valve seat, a spring for urging the valveelement toward the valve seat, and a slidable sealing member disposed ina sliding portion of the valve element.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description when takenin conjunction with the accompanying drawings which illustrate preferredembodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional view showing the constructionof a switching valve according to a first embodiment, with its solenoidbeing OFF.

FIG. 2 is a longitudinal cross-sectional view showing the constructionof the switching valve according to the first embodiment, with itssolenoid being ON.

FIG. 3 is a longitudinal cross-sectional view showing the constructionof a switching valve according to a second embodiment, with its solenoidbeing OFF.

FIG. 4 is a longitudinal cross-sectional view showing the constructionof the switching valve according to the second embodiment, with itssolenoid being ON.

FIG. 5 is a longitudinal cross-sectional view showing the constructionof a switching valve according to a third embodiment, with its solenoidbeing OFF.

FIG. 6 is a longitudinal cross-sectional view showing the constructionof the switching valve according to the third embodiment, with itssolenoid being ON.

FIG. 7 is a longitudinal cross-sectional view showing the constructionof a switching valve according to a fourth embodiment, with its solenoidbeing OFF.

FIG. 8 is a longitudinal cross-sectional view showing the constructionof the switching valve according to the fourth embodiment, with itssolenoid being ON.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings.

FIG. 1 is a longitudinal cross-sectional view showing the constructionof a switching valve according to a first embodiment, with its solenoidbeing OFF. FIG. 2 is a longitudinal cross-sectional view showing theconstruction of the switching valve according to the first embodiment,with its solenoid being ON.

The switching valve includes the inlet port 2 formed in a side of a body1, for introducing refrigerant fed under pressure from a compressor, andthe first outlet port 3 and a second outlet port 4 for sending theintroduced refrigerant selectively to a condenser or an evaporator,respectively. A cylinder bore communicating with the inlet port 2 hasthe movable plug 5 disposed therein in a vertically movable manner, asviewed in the figure. Below the movable plug 5, as viewed in the figure,there is provided a hollow cylindrical valve seat 6 integrally formedwith the body 1 in a manner opposed to the movable plug 5. The valveseat 6 has a valve hole communicating with the first outlet port 3. Themovable plug 5 has an annular valve sheet 7 disposed at a portionthereof via which the movable plug 5 is seated on the valve seat 6. Thevalve sheet 7 is held on the movable plug 5 by a washer 8 and a swagedportion of the movable plug 5. The valve sheet 7 is made of a flexiblematerial so as to enhance sealing performance exhibited when the movableplug 5 is seated on the valve seat 6. Preferably, the valve sheet 7 canbe formed by a sealing member made of polytetrafluoroethylene. Further,on the outer periphery of the movable plug 5, there are provided apiston ring 9 that slides on an inner wall of a cylinder boreaccommodating the movable plug 5, and a tension ring 9 a for radiallyoutwardly urging the piston ring 9. A spring 10 is disposed in a backpressure chamber for the movable plug 5, for urging the movable plug 5in a direction in which the movable plug 5 is seated on the valve seat6.

A pilot valve is disposed above the cylinder bore accommodating themovable plug 5. The pilot valve comprises a valve portion forcontrolling whether or not the back pressure chamber for the movableplug 5 should be communicated with the first outlet port 3 via a passage11 formed in the body 1, and a solenoid. The valve portion includes afixed plug 12 which is configured to close the upper opening of thecylinder bore accommodating the movable plug 5 and has a valve hole in acenter thereof, and a valve sheet 13 which is disposed in a mannermovable to and away from a pilot valve seat formed by raising the rim ofthe upper opening of the valve hole, to thereby form a pilot valveelement. The fixed plug 12 has an O ring 14 fitted on an outer peripherythereof, for sealing between the fixed plug 12 and the inner wall of thecylinder bore accommodating the fixed plug 12.

Above the fixed plug 12, there is provided a cap 15 disposed to closethe upper opening of the body 1. The cap 15 is prevented from beingremoved from the body 1, by a C ring 16, and an O ring 17 seals betweena space communicating with the passage 11 and the atmosphere. Thesolenoid for actuating the pilot valve comprises a sleeve 18 fitted inthe central opening of the cap 15, a plunger 19 axially movably disposedin the sleeve 18 and holding the valve sheet 13 forming the pilot valveelement at an end thereof, a core 20 provided for closing the upper endof the sleeve 18, a spring 21 disposed between the plunger 19 and thecore 20, for urging the plunger 19 toward the fixed plug 12, a solenoidcoil 22 circumferentially arranged outside the sleeve 18, and a yoke 23disposed in a manner surrounding the solenoid coil 22. Thus, the abovearrangement constructs a pilot-operated solenoid valve, that is, a firstvalve of the switching valve.

Further, a second valve of the switching valve disposed between theinlet port 2 and the second outlet port 4 has a hollow cylindrical valveseat 24 integrally formed with the body 1 in an intermediate portion ofa passage communicating between the inlet port 2 and the second outletport 4, and a movable plug 25 disposed movably from the side of thesecond outlet port 4 in a manner opposed to the valve seat 24. The valveseat 24 has a valve hole having substantially the same diameter as thatof the valve seat 6 of the first valve. The movable plug 25 has anannular valve sheet 26 disposed at a portion thereof opposed to thevalve seat 24. The valve sheet 26 is held on the movable plug 25 by awasher 27 and a swaged portion of the movable plug 25. Further, on theouter periphery of the movable plug 25, there is provided an X packing28 made of a rubber or a resin, which seals between the movable plug 25and the inner wall of a cylinder bore accommodating the movable plug 25while sliding on the inner wall of the cylinder bore. By using theslidable X packing 28 as a sealing member, it is possible to set a largeopening stroke of the second valve, to thereby reduce pressure lossoccurring when the refrigerant passes through the second valve. The backpressure chamber for the movable plug 25 communicates with the firstoutlet port 3 via a passage 29, and has a spring 30 disposed therein forurging the movable plug 25 toward the valve seat 24. The cylinder boreaccommodating the movable plug 25 has a lower opening thereof closed bya cap 31. The cap 31 is prevented from being removed from the body 1 bya C ring 32, and an O ring 33 seals between the back pressure chamberand the atmosphere.

In the switching valve constructed as above, when the solenoid coil 22is in a deenergized state, i.e. when the solenoid is OFF, with norefrigerant being introduced into the inlet port 2, no solenoid forcefor actuating the pilot valve is generated, so that the plunger 19 ispushed downward as viewed in the figure by the spring 21, whereby thevalve sheet 13 is seated on the pilot valve seat of the fixed plug 12.Since this causes the pilot valve to be in a closed state, the passage11 leading from the back pressure chamber above the movable plug 5 tothe first outlet port 3 is blocked. Further, the movable plug 25 ispushed upward by the spring 30, to thereby also block communicationbetween the inlet port 2 and the second outlet port 4.

In the above state, when high-pressure refrigerant is introduced fromthe compressor into the inlet port 2, the pressure of the refrigerantattempts to push upward the movable plug 5 of the first valve, and topush downward the movable plug 25 of the second valve, to thereby act toopen both of the first and second valves. However, in the first valve,part of the refrigerant introduced into the inlet port 2 enters the backpressure chamber for the movable plug 5 via the piston ring 9, so thatthe back pressure chamber for the movable plug 5 comes to have the samepressure as the pressure in the inlet port 2. As a result, as shown inFIG. 1, the movable plug 5 is urged toward the valve seat 6 by thespring 10 to thereby close the first valve. The closing of the firstvalve causes the movable plug 25 to receive high pressure on a sidethereof toward the inlet port 2, and low pressure from the first outletport 3 on a back pressure side thereof, so that the movable plug 25 ispushed downward by the differential pressure therebetween, whereby thesecond valve is placed in its valve-open state.

Next, when the solenoid coil 22 is energized, i.e. when the solenoid isON, as shown in FIG. 2, the plunger 19 of the solenoid is pulled by thecore 20, whereby the valve sheet 13 held on the plunger 19 is moved awayfrom the valve seat formed on the fixed plug 12. This causes the backpressure chamber for the movable plug 5 to communicate with the firstoutlet port 3 via the passage 11, so that the pressure in the backpressure chamber is reduced, whereby the movable plug 5 is pushed upwardby the pressure of the high-pressure refrigerant introduced into theinlet port 2. As a result, the valve sheet 7 held on the movable plug 5is moved away from the valve seat 6 to thereby open the first valve. Onthe other hand, as for the second valve, the pressure in the backpressure chamber for the movable plug 25, which communicates with thefirst outlet port 3 via the passage 29, becomes equal to that at theinlet port 2 due to opening of the first valve. Since the movable plug25 is urged toward the valve seat 24 by the spring 30, the valve sheet26 held on the movable plug 25 is seated on the valve seat 24 to therebyclose the second valve. When the valve sheet 26 is seated on the valveseat 24, the movable plug 25 has a pressure-receiving area on the sidethereof toward the inlet port 2, which is equal to the cross-sectionalarea of the valve hole surrounded by the valve seat 24, and apressure-receiving area on the back pressure side, which is equal to thecross-sectional area of the movable plug 25. This causes a force to actin the direction of closing of the second valve and the urging force ofthe spring 30 is also additionally applied, whereby the closed state ofthe second valve is maintained.

As described above, this switching valve is constructed to operate suchthat the second valve is opened by the differential pressure generatedby closing of the first valve operated by the solenoid, and thedifferential pressure is reduced to zero by opening of the first valve,but the second valve is closed by the spring 30. After the second valveis closed, the valve-closed state is held by the spring 30 and thedifference between the pressure-receiving areas. Further, both the firstvalve and the second valve holes have substantially the same diameterand the opening stroke thereof can be increased, so that it is possibleto reduce pressure loss. Further, by using the slidable sealing memberin the sealing structure of the second valve, it is possible to easilyincrease the opening stroke of the second valve moved by the abovedifferential pressure, without increasing the size of the body 1. Thismakes it possible to form a switching valve having a space-savingstructure.

FIG. 3 is a longitudinal cross-sectional view showing the constructionof a switching valve according to a second embodiment, with its solenoidbeing OFF. FIG. 4 is a longitudinal cross-sectional view showing theconstruction of the switching valve according to the second embodiment,with its solenoid being ON. In these figures, component elements havingidentical or equivalent functions to those of the component elementsshown in FIG. 1 and FIG. 2 are designated by the same referencenumerals, and detailed description thereof is omitted.

The switching valve according to the second embodiment is distinguishedfrom the switching valve according to the first embodiment in which afirst valve thereof is of a normally closed type which is closed whenthe solenoid is OFF, in that the first valve of the switching valveaccording to the second embodiment is of a normally open type.

The solenoid of the switching valve according to the second embodimentis constructed such that the core 20 is integrally formed with the cap15 of the switching valve according to the first embodiment, with aflange portion thereof being disposed in a manner closing the upperopening of the body 1, and is rigidly fixed to the body 1 by the C ring16. The solenoid has the plunger 19 thereof disposed within the sleeve18 outside the core 20.

The core 20 has a cylinder bore which opens downward and a plug 34 isaxially movably disposed therein. The plug 34 holds the valve sheet 13at a lower portion thereof, and is urged in a direction in which itmoves away from a valve seat formed on the fixed plug 12, by the spring21 disposed between the plug 34 and the fixed plug 12. A shaft 35extending through the core 20 is arranged between the plug 34 and theplunger 19. Due to this construction, when the solenoid is OFF, theurging force of the spring 21 is transmitted to the plunger 19 via theplug 34 and the shaft 35 to thereby move the plunger 19 away from thecore 20. When the solenoid is turned ON, the solenoid force generated bypulling of the plunger 19 toward the core 20 is transmitted to the plug34 via the shaft 35 to cause the valve sheet 13 held on the plug 34 tobe seated on the valve seat formed on the fixed plug 12.

In the switching valve constructed as above, when high-pressurerefrigerant is introduced into the inlet port 2 in a state of thesolenoid being OFF, since the pilot valve is open to cause the backpressure chamber for the movable plug 5 to communicate with the firstoutlet port 3 at low pressure, the movable plug 5 is easily pushedupward by the pressure of the refrigerant, whereby the first valve isopened. At this time, the movable plug 25 is pushed downward by thepressure of the refrigerant and is about to open the second valve.However, due to opening of the first valve, pressure on a downstreamside of the first valve is increased, and the increased pressure isintroduced into the back pressure chamber for the movable plug 25 viathe passage 29, so that the movable plug 25 causes the valve sheet 26 tobe seated on a valve seat 24 by the upward urging force of the spring30. After that, the second valve is held in its valve-closed state bythe high pressure introduced into the back pressure chamber for themovable plug 25.

When the solenoid is turned ON, as shown in FIG. 4, the plunger 19 ofthe solenoid is pulled by the core 20, whereby the plunger 19 pushesdownward the plug 34 via the shaft 35 to cause the valve sheet 13 heldon the plug 34 to be seated on the valve seat formed on the fixed plug12. Due to closing of the pilot valve, part of the refrigerant isintroduced into the back pressure chamber for the movable plug 5 via thepiston ring 9, so that the pressure in the back pressure chamber isabout to have the same pressure as that in the inlet port 2. As aresult, the movable plug 5 is pushed downward by the spring 10, wherebythe valve sheet 7 is seated on the valve seat 6 to close the firstvalve. When the first valve is closed, the pressure in the first outletport 3 is reduced, and the pressure in the back pressure chamber for themovable plug 25 is also reduced. Accordingly, the movable plug 25 ispushed downward by the high-pressure refrigerant, whereby the secondvalve is opened.

FIG. 5 is a longitudinal cross-sectional view showing the constructionof a switching valve according to a third embodiment, with its solenoidbeing OFF. FIG. 6 is a longitudinal cross-sectional view showing theconstruction of the switching valve according to the third embodiment,with its solenoid being ON. In these figures, component elements havingidentical or equivalent function to those of the component elementsshown in FIG. 1 and FIG. 2 are designated by the same referencenumerals, and detailed description thereof is omitted.

The switching valve according to the third embodiment is distinguishedfrom the switching valve according to the first embodiment in that asecond valve thereof is disposed on the upstream side of the valve seat24. In this embodiment, similarly to the movable plug 5 of the firstvalve, the movable plug 25 of the second valve is movably disposed inthe cylinder bore communicating with the inlet port 2. Therefore, whenthe second valve is in its valve-closed state, the pressure-receivingarea of the movable plug 25 where the pressure of refrigerant isreceived is equal to an area obtained by subtracting the cross-sectionalarea of the valve hole surrounded by the valve seat 24 from thecross-sectional area of the movable plug 25. Since the area is smallerthan the pressure-receiving area of the movable plug 25 where thepressure of refrigerant is received from the back pressure chamber, thevalve-closed state of the second valve can be maintained when the firstvalve is open and the second valve is closed.

In the switching valve constructed as above, when the solenoid is OFF,the pilot valve is in its valve-closed state. When high-pressurerefrigerant is introduced into the inlet port 2, as shown in FIG. 5,first, in the first valve, the movable plug 5 is about to be movedupward by the pressure of the refrigerant introduced into the inlet port2, but since part of the refrigerant enters the back pressure chamberfor the movable plug 5 via the piston ring 9, whereby the pressure inthe back pressure chamber for the movable plug 5 becomes equal to thepressure in the inlet port 2, so that the movable plug 5 is urged by thespring 10 toward the valve seat 6 to close the first valve. This causesthe first outlet port 3 to be reduced in pressure, and hence the movableplug 25 is pushed downward by the pressure of the refrigerantintroduced, whereby the second valve is opened.

When the solenoid is turned ON, as shown in FIG. 6, the pilot valve isopened to cause the back pressure chamber for the movable plug 5 tocommunicate with the first outlet port 3 via the passage 11, whereby theback pressure chamber for the movable plug 5 is reduced in pressure.This causes the movable plug 5 to be pushed upward by the pressure ofthe high-pressure refrigerant introduced into the inlet port 2 to openthe first valve. When the first valve is opened, the pressure in theback pressure chamber for the movable plug 25, which communicates withthe first outlet port 3 via the passage 29, becomes equal to thepressure in the inlet port 2, so that the movable plug 25 is pushedupward by the spring 30, to close the second valve.

FIG. 7 is a longitudinal cross-sectional view showing the constructionof a switching valve according to a fourth embodiment, with its solenoidbeing OFF. FIG. 8 is a longitudinal cross-sectional view showing theconstruction of the switching valve according to the fourth embodiment,with its solenoid being ON. In these figures, component elements havingidentical or equivalent capabilities to those of the component elementsshown in FIGS. 5 and 6 are designated by the same reference numerals,and detailed description thereof is omitted.

The switching valve according to the fourth embodiment is distinguishedfrom the switching valves according to the first to third embodiments inthat the sealing structure of the second valve is changed from the Xpacking 28 having sliding resistance into a sealing structure havingsubstantially no sliding resistance.

The second valve has a third valve disposed on the back pressure chamberside thereof, for isolating the sliding portion thereof and the backpressure chamber therefor from each other when the second valve isopened. More specifically, the movable plug 25 of the second valve has alower end face thereof integrally formed with an annular projection 36forming a valve element. On an end face of the cap 31 opposed to theannular projection 36 is arranged an annular valve sheet 37 forming avalve seat such that it forms a third valve together with the annularprojection 36. The cap 31 has the passage 29 a formed through a centralportion thereof surrounded by the valve sheet 37, and opening into theback pressure chamber of the second valve. The passage 29 a is formedsuch that it extends through the cap 31 to communicate with the passage29 formed in the body 1. Further, the cap 31 has an O ring 38 fitted onan outer periphery thereof on a side toward the second valve, forpreventing refrigerant from leaking into the passage 29 via the slidingportion of the movable plug 25 when the second valve is open and thethird valve is closed.

Thus, the sealing of the sliding portion of the movable plug 25, whichis required when the second valve is open, is made by using the annularprojection 36 and the valve sheet 37. This makes it possible to dispensewith the X packing 28 which is required for preventing internal leakageof refrigerant from the movable plug 25 of each of the switching valvesaccording to the first to third embodiments, thereby making the movableplug 25 easy to move. Further, in the second valve according to thepresent embodiment, it is possible to reduce the spring force of thespring 30, which is required for urging the movable plug 25 in thevalve-closing direction by overcoming the sliding resistance of the Xpacking 28. Furthermore, since the spring force of the spring 30 forurging the movable plug 25 in the valve-closing direction is reduced, aforce attempting to close the second valve when it is open is reduced,which makes it possible to further reduce pressure loss of therefrigerant when the refrigerant passes through the second valve.

In the switching valve constructed as above, when the solenoid is OFF,the pilot valve is in its valve-closed state. When high-pressurerefrigerant is introduced into the inlet port 2, as shown in FIG. 7,first, in the first valve, the movable plug 5 is about to be pushedupward by the pressure of the refrigerant introduced into the inlet port2, but part of the refrigerant enters the back pressure chamber for themovable plug 5 via the piston ring 9, making the pressure in the backpressure chamber for the movable plug 5 equal to the pressure in theinlet port 2, which causes the movable plug 5 to be urged by the spring10 toward the valve seat 6 to close the first valve. This causes thepressure in the first outlet port 3 to be reduced, and hence the movableplug 25 is pushed downward by the pressure of the refrigerantintroduced, whereby the second valve is opened. At this time, the thirdvalve, which comprises the annular projection 36 and the valve sheet 37and is provided on the back pressure chamber side of the second valve,is closed, whereby it is possible to prevent the refrigerant fromflowing from the inlet port 2 at high pressure to the first outlet port3 at low pressure via the sliding portion of the movable plug 25 and thepassage 29.

When the solenoid is turned ON, as shown in FIG. 8, the pilot valve isopened to cause the back pressure chamber for the movable plug 5 tocommunicate with the first outlet port 3 at low pressure via the passage11. This causes the movable plug 5 to be pushed upward by the pressureof the high-pressure refrigerant introduced into the inlet port 2 tothereby open the first valve. When the first valve is opened, thepressure in the back pressure chamber for the movable plug 25, whichcommunicates with the first outlet port 3 via the passages 29, 29 a,becomes equal to the pressure in the inlet port 2, so that the movableplug 25 is pushed upward by the spring 30, to close the second valve.

Although in the first valve and the second valve in each of the aboveembodiments, the valve seats 7, 26 for enhancing sealing performancewhen the first and second valves are closed are arranged on the movableplugs 5, 25, respectively, they may be provided on the their valveseats.

Further, although in the first to third embodiments, the X packing isused as the slidable sealing member of the second valve, it is alsopossible to use an O ring.

Moreover, although it is only a matter of course that the presentinvention can be applied to a refrigerant passage-switching part whichhas one inlet port and is required to selectively switch between twooutlet ports, in the refrigeration cycle disclosed e.g. in theaforementioned Japanese Unexamined Patent Publication No. 2000-318436(Paragraph No. [0016], FIG. 1) or Japanese Unexamined Patent PublicationNo. 2002-211234, the present invention can be also applied to arefrigerant passage-switching part for bypassing one heat exchanger.

As described above, the switching valve according to the presentinvention is constructed to operate such that a second valve is openedby a differential pressure generated by closing of a first valveoperated by a solenoid, and when the first valve is opened, thedifferential pressure is reduced to zero, but the second valve is closedby a spring, whereafter the valve-closed state is maintained by thespring and the difference between receiving areas. This makes itpossible to increase the opening stroke while forming the first valveand the second valve such that they have valve holes having the samediameter, and thereby reduce pressure loss while saving space.

Further, by using a slidable seal in the second valve, more space can besaved than when a diaphragm-type differential pressure valve is used.

Alternatively, by providing a third valve for sealing a sliding portionof the second valve on a back pressure chamber side thereof, it ispossible not only to save more space than when a diaphragm-typedifferential pressure valve is used but also to reduce the slidingresistance of the second valve, which makes it possible to furtherreduce the pressure loss in the second valve.

The foregoing is considered as illustrative only of the principles ofthe present invention. Further, since numerous modifications and changeswill readily occur to those skilled in the art, it is not desired tolimit the invention to the exact construction and applications shown anddescribed, and accordingly, all suitable modifications and equivalentsmay be regarded as falling within the scope of the invention in theappended claims and their equivalents.

1. A switching valve for causing refrigerant introduced into an inletport to flow selectively to a first outlet port or a second outlet port,characterized by comprising: a solenoid-operated first valve that opensand closes a refrigerant passage between said inlet port and said firstoutlet port; a second valve that is disposed in a refrigerant passagebetween said inlet port and said second outlet port, and is opened by adifferential pressure generated by closing of said first valve; and athird valve for isolating a sliding portion of said second valve and aback pressure chamber for said second valve, from each other, therebysealing between a downstream side of said first valve and an upstreamside of said second valve, when said second valve is opened.
 2. Theswitching valve according to claim 1, wherein said third valve has anannular projection integrally formed with a valve element of said secondvalve on a side of said second valve toward a back pressure chamber, anda valve seat disposed in a manner opposed to said annular projectionsuch that said valve seat surrounds an opening of a passagecommunicating with the downstream side of said first valve, which opensinto said back pressure chamber.